矿床地球化学国家重点实验室知识库

New analyses of siderophile–lithophile elements and Sr–Nd isotopes in the Permian basalts and picrites from northern Vietnam, the southernmost occurrence of the Emeishan flood basalt province, together with previously published data, are used to address the question of whether any meaningful correlation between these elements and isotopes exists at a province scale. The available data show that negative correlations between ε_Nd, (⁸⁷Sr/⁸⁶Sr)_i and mantle-normalized (Nb/Th)_n are present in the basalts but not in the associated picrites. This indicates that crustal contamination is negligible in the picrites but significant in some of the basalts. The picrites and basalts from the entire province show negative correlations between (Rh/Ru)_n, (Pt/Ru)_n, (Pd/Ru)_n and Mg-number. This indicates that Ru behaves compatibly whereas Rh, Pt and Pd behave incompatibly during magma differentiation. The incompatible behavior of Rh in natural basaltic systems is also supported by the fact that (Pt/Rh)_n remains constant with decreasing Mg-number in the lavas. Depletions of Pd and Pt, and to a lesser degree Cu, in some basaltic samples characterized by relatively low ε_Nd and (Nb/Th)_n support the notion that sulfide saturation in the magmas was triggered by a combination of siliceous crustal contamination and addition of external sulfur. Within the entire flood basalt province only the picrites from Song Da, northern Vietnam show clear depletion in Ir relative to Ru. These picrites are also characterized higher Al₂O₃/TiO₂ and lower mantle-normalized La/Yb (0.2–2.4) than those from elsewhere in the province, possibly due to the involvement of an Ir-depleted, fertile mantle component in magma generation at this location.